The inventions relates generally to grinding machines employing a dressing roll unit for conditioning the grinding wheel.
In particular, the invention concerns itself with roll-type dressing units wherein the roll is of the powered type, i.e. the roll has its own motorized assembly for imparting rotational motion to the roll before and during contact with the grinding wheel. Such dressing units are well-known in the grinding arts and are expensive and difficult to make, particularly for wide dressing paths. Of important consideration is a centerless grinding machine, where grinding wheels can typically be, up to 24 inches wide. In conditioning a wheel of this width, a comparable length dressing roll must be employed, and, the main portion of roll support is obtained at or near the ends. In all cases, the roll must rotate. However, in certain assemblies the roll is attached to a shaft which is rotated in bearings at its ends, typically ball bearing sets. In such mounting stance, the shaft behaves as if it were a "simply supported" beam, assuming a classical deflection curve through what may be indicated as "points" of suspension at its ends.
In one prior art assembly, U.S. Pat. No. 4,206,953, the dressing roll in a wide wheel dressing unit is generally tubular, and is supported on a nonrotating shaft. The shaft is held at its ends in a dressing unit housing, and the rotational support bearings comprise a plurality of pockets machined in the outer surface of bushings located on the shaft. The pockets are supplied with high pressure oil which, in typical hydrostatic bearing fashion, is supplied through a series of restrictors to each pocket. Thus, the classical hydrostatic bearing is achieved, which is self-compensating for deflection around the pocket areas. The truing assembly of the prior art suffers from several infirmities including the necessity of supplying high pressure oil or other fluid to the bearing area and attendant pump requirements and leakage potential; the necessity of utilizing a restrictor, such as an orifice or choke coil, which may become clogged and unable to function properly; and the fact that the nonrotating shaft has relatively small end diameters and is, apparently, slid into the housing bores and locked in position. This style of assembly for the shaft does not provide the maximum stiffness.
In contrast, applicants have obviated the difficulties inherent in the prior art devices by their design of a roll-type dressing unit, in which a relatively stationary casting is provided with very thick walls to support the shafts, and the shaft spanning the two walls is tightly clamped and thus approaching what is classically described as a "fixed end" beam -- that is, one having a very shallow deflection curve across its length when compared with a "simple-supported" beam. Further, applicants have designed a hydrodynamic bearing system directly into the shaft at spaced-apart points, that is, where the roll body is created with accurately bored end bushings and the bushings form an annular space around the hydrodynamic bearing points. A plurality of wedge-like reliefs are formed into the shaft surface, all going in the same direction. Low pressure oil is flowed through the roll body and, during high rotational speed of the roll a hydrodynamic wedge of oil will be driven into the wedge formations, creating an extremely stiff bearing system which, when coupled with the "fixed end" beam support system, creates an overall system of enhanced rigidity without the need for loose, pivoting bearing parts found in prior art hydrodynamic bearings.
It is therefore an object of the present invention to provide a roll-type dressing unit having an extremely stiff roll support system.